1. Field of the Invention
This invention relates to a novel structure of laminated rubber stopper and more particularly, it is concerned with a laminated rubber stopper used for sealing containers, instruments, etc. for medicaments and medical treatments.
2. Description of the Prior Art
As a stopper material of a container, instrument, etc. for medicaments and medical treatments, it is desired to have various properties such as heat resistance, compression resistance test, softness, chemical inertness and low permeability of gases or water. In particular, rubbers are excellent in sealing property and natural rubbers have been used for a long time while synthetic rubbers have often been used more recently for example, isobutylene-isoprene co-polymer rubbers (IIR) having been recommended from a sanitary point of view. However, these materials have such problems as contamination in that curing agents, compounding agents, etc. contained in rubbers are dissolved in medicaments held in containers, the contents in a container are adsorbed on the rubber surface, fine grains occur from the rubber material during the production process or storage, etc.
In order to solve these problems, a laminated rubber stopper has been proposed in which a part of the rubber stopper, to be contacted with a contents in a container, or the whole surface of a leg part is laminated with a chemically inert resin such as fluoro resins. The contamination due to contact of a liquid medicament, etc., with a rubber surface can be prevented by the laminated rubber stopper, but in fact, such a proposal cannot be applied to preparation of drugs since there arise new problems that the leg part of the stopper laminated with a fluoro resin, etc. is inferior in sealing property of the mouth part of a vial to that having a rubber surface exposed and preparation of a thin laminated layer capable of maintaining rubber elasticity is difficult.
As shown in FIG. 5, on the other hand, the inventor has proposed a laminated rubber stopper capable of preventing the contamination by forming a laminated layer of a fluoro resin film on a leg part, while maintaining the tightness or sealing property with a container by retaining an exposed rubber surface on an area from the lower surface of a flange part in the top part of a rubber stopper body to the base of the leg part (Japanese Patent Publication No. 64062/1993), and a production process for realizing this structure (Japanese Patent Publication No. 50386/1993).
The above described laminated rubber stopper the inventor has proposed is an excellent rubber stopper capable of realizing the desired effects, but this cannot be said to be suitable for application to a container for a very unstable and expensive medicament, for example, biotechnological preparations, anticancer drugs, etc., which have lately been developed, since a rubber surface is contacted with a lip part of a container although it is not contacted with a liquid medicament. For the production thereof, a complicated process is required the stopper, using upper and lower metallic molds, thus increasing the production cost.